With the advent of high speed thermoplastic bag making machines the need for a variety of controls became essential to produce high quality bags and bags of various varieties. Present day high speed bag machines can operate, for certain bag dimensions and bag styles, up to 300 bags a minute. At such speeds it is essential that the bags are accumulated in stacks containing a pre-determined number of bags and that the bags in each stack are accumulated so that the respective bag edges are in vertical alignment much like a deck of cards. To achieve alignment of the successive bags to produce neatly registered bag stacks it is essential that the velocity of the bag is reduced as it approaches the stack-forming gates or abutments which are located on a table adjacent to the discharge end of the bag machine.
To achieve this result the present invention includes a device operable in time relation with the cycle rate of the bag machine for retarding the velocity of the bags. The basic arrangement of the subject matter of the present invention is disclosed in U.S. Pat. No. 3,722,376 issued Mar. 27, 1973 and assigned to the assignee of the present invention. By reference to this patent it is intended that its disclosure is incorporated herein. As shown in the referenced patent, after the leading portion of the plastic web has been severed and sealed by a heated seal bar, a bag is produced and it is received by stacker belts that transport the bag to a table that accumulates the bags in stacks. As the bag is discharged by the stacker belts, it encounters corrugating rollers which essentially consist of a lower and upper shaft mounting discs which are staggered relative to each other so as to impart a slight wavy configuration to the bags. This provides the bags with a certain amount of stiffness in the direction of bag transport.
Adjacent the corrugating device bag machines incorporate transverse simultaneously driven vertically spaced shafts which include radial projections mounting longitudinally extending pads that momentarily make contact with the trailing edge of the bags in order to reduce its velocity. Such a reduction of velocity, considering the thin filmy character of some of the plastic bags, reliably prevents "floating" and of course insures that the bag travels in a downwardly sloping path to the location where a bag stack is being accumulated. While the bag retarding or slow down device of the prior art has served reasonably well for bag machine speeds of up to 200 cycles per minute, it has been found that above such rate a slow-down device with one projecting pad on each shaft cannot be operated in the proper synchronism to retard bags produced at machine speeds in excess of 200 cycles per minute.